Toothbrushes are well-known articles and normally comprise a head and a grip handle, generally with a narrowed neck region in between, all arranged along a longitudinal head-handle axis. Normally toothbrushes are made primarily of a hard plastic material, e.g. a polypropylene or styrol acryl nitrol (“SAN”). Many are so called two-component toothbrushes, i.e. comprising parts made of hard plastic, e.g. the head and the main structure or “skeleton” of the handle, and parts made of a softer resilient elastomer or rubbery material, such as a thermoplastic elastomer e.g. Santoprene™ e.g. comprising part of the grip handle, to enhance grip, aesthetic appearance or to influence flexibility. Such toothbrushes are disclosed for example in U.S. Pat. No. 5,054,154 and EP-A-0 336 641 among others.
Toothbrushes are normally made by an injection moulding process in which the hard plastic material of which their main structure is made is injected in a fluid state into a first mould cavity which accurately defines the shape of the hard plastic part to be formed. The mould cavity is normally formed in a hard metal (usually steel) mould block, using a process of spark-erosion also known as electro-discharge machining. Normally when the toothbrush head is formed in such a process pins are provided (“bristle pins”) projecting onto the part of the cavity in which the head is to be formed, to form holes in the plastic material of the head into which tufts of bristles can subsequently be fixed. With two component toothbrushes a “skeleton” of hard plastic is first made in this way then the skeleton is enclosed in a second mould cavity and the material of the second component in a fluid state is injected into this second cavity to form the second component parts. Normally the skeleton is formed with voids to receive this second material. Normally such injection moulds are mould assemblies comprising one or more, generally two, mould blocks each with a part mould cavity therein, which when brought together in the assembled mould define a complete mould cavity between them. Such processes are well known. WO-A-94/05183, EP-A-0 504 571, EP-A-0 836 923 and DE-A-195 22 122 describe such processes and suitable moulding machinery for their performance.
Generally such moulding processes involve large and complex machinery and such machines can take up much floor space in a factory. It is desirable to provide improved moulding machinery for such processes. So called stack moulds are known which can be made very compact. For example U.S. Pat. No. 5,069,615 discloses a stack mould for making plastic articles.